1. Field of the Invention
The present invention relates to a comparator circuit and more particularly to a comparator circuit, which determines the magnitudes of voltage levels of a comparison input signal increasing or decreasing monotonously and a reference input signal.
2. Description of the Related Art
As an example of a characteristic correction circuit for correcting the characteristic of an analog circuit depending on an external factor such as temperature, a primary characteristic correction circuit, which uses two primary coefficients intersecting in a threshold value, can be mentioned. A characteristic correction circuit 110 shown in FIG. 16 comprises a comparator circuit 100 which compares a comparison input signal IN which is a temperature detection value with a reference input signal REF set preliminarily, a coefficient selective operating portion 113 which selects one of a first correction coefficient 111 and a second correction coefficient 112 depending on a comparison result of the comparator circuit 100 and computes its correction value and a correction portion 114 for correcting the characteristic of an analog circuit 120 depending on the correction value. Upon correction of the characteristic of the analog circuit 120, the respective correction coefficients 111, 112 are switched by the comparator circuit 100 when the voltage level of the comparison input signal IN and the voltage level of the reference input signal REF meet each other.
This characteristic correction circuit 110 often corrects the characteristic corresponding to a slowly changing phenomenon such as the surrounding environment and temperature in the circuit. The comparator circuit 100 of the characteristic correction circuit 110 which corrects for the temperature amplifies a fine detection output such as noise and outputs an oscillation waveform because the comparison input signal IN changes slowly in the vicinity of the threshold. If the oscillation waveform is outputted from the comparator circuit 100, the coefficient selective operation portion 113 and the correction portion 114 cannot follow up such a quick change so that they cannot correct the characteristic properly. Thus, there is a problem in that an abnormal voltage may be outputted from the analog circuit.
To solve such a problem, the comparator circuit 100 having hysteresis characteristic is sometimes used in order to suppress an output of the oscillation waveform in the comparator circuit 100 in the vicinity of the threshold. The comparator circuit 100 having the hysteresis characteristic has different thresholds between a case where a detection value as an external factor changes upward and a case where it changes downward. As a consequence, the comparator circuit 100 becomes unlikely to be affected by fine voltage changes such as noise, so as to suppress an output of the oscillation waveform of the comparator circuit 100.
As regards the comparator circuit 100, related arts have been disclosed in Japanese Unexamined Patent Publication No.60 (1985)-186764 and Japanese Unexamined Patent Publication No. 2001-34366.